Context: Pancreatic α-amylase and α-glucosidase inhibitors serve as important strategies in the management of blood glucose. Even though Syzygium cumini (L.) Skeels (Myrtaceae) (SC) is used extensively to treat diabetes; scientific evidence on antidiabetic effects of SC leaves is scarce. Objective: SC leaf extract was investigated for α-amylase inhibitory effect and continued with isolation and identification of α-amylase inhibitors. Materials and methods: Bioassay-guided fractionation was conducted using in vitro α-amylase inhibitory assay (with 20–1000 μg/mL test material) to isolate the inhibitory compounds from ethyl acetate extract of SC leaves. Structures of the isolated inhibitory compounds were elucidated using 1H NMR and 13C NMR spectroscopic analysis and direct TLC and HPLC comparison with authentic samples. Study period was from October 2013 to October 2015. Results: An active fraction obtained with chromatographic separation of the extract inhibited porcine pancreatic α-amylase with an IC50 of 39.9 μg/mL. Furthermore, it showed a strong inhibition on α-glucosidase with an IC50 of 28.2 μg/mL. The active fraction was determined to be a 3:1 mixture of ursolic acid and oleanolic acid. Pure ursolic acid and oleanolic acid showed IC50 values of 6.7 and 57.4 μg/mL, respectively, against α-amylase and 3.1 and 44.1 μg/mL respectively, against α-glucosidase. Discussion and conclusions: The present study revealed strong α-amylase and α-glucosidase inhibitory effects of ursolic acid and oleanolic acid isolated from SC leaves for the first time validating the use of SC leaves in antidiabetic therapy.
BackgroundHyperglycaemia is a salient feature of poorly controlled diabetes mellitus. Rate of protein glycation is increased with hyperglycaemia leading to long term complications of diabetes. One approach of controlling blood glucose in diabetes targets at reducing the postprandial spikes of blood glucose. The objectives of this study were to assess the in vitro inhibitory effects of Costus speciosus (COS) leaves on α-amylase and α-glucosidase activities, fructosamine formation, protein glycation and glycation-induced protein cross-linking.MethodsMethanol extracts of COS leaves were used. Inhibitory effects on enzyme activities were measured using porcine pancreatic α-amylase and α-glucosidase from Saccharomyces cerevisiae in the presence of COS extract. Percentage inhibition of the enzymes and the IC50 values were determined. In vitro protein glycation inhibitory effect of COS leaves on early and late glycation products were measured using bovine serum albumin or chicken egg lysozyme with fructose. Nitroblue tetrazolium was used to assess the relative concentration of fructosamine and polyacrylamide gel electrophoresis was used to assess the degree of glycation and protein cross-linking in the reaction mixtures.Resultsα-Glucosidase inhibitory activity was detected in COS leaves with a IC50 of 67.5 μg/ml which was significantly lower than the IC50 value of Acarbose (p < 0.01). Amylase inhibitory effects occurred at a comparatively higher concentration of extract with a IC50 of 5.88 mg/ml which was significantly higher than the IC50 value of Acarbose (p < 0.01). COS (250 μg/ml) demonstrated inhibitory effects on fructosamine formation and glycation induced protein cross-linking which were in par with 1 mg/ml aminoguanidine were detected.ConclusionMethanol extracts of COS leaves demonstrated in vitro inhibitory activities on α-glucosidase, fructosamine formation, glycation and glycation induced protein cross-linking.These findings provide scientific evidence to support the use of COS leaves for hypoglycemic effects with an added advantage in slowing down protein glycation.
Glycation is a prime mechanism responsible for chronic diabetic complications, a process which is enhanced under hyperglycaemia. Natural inhibitors of protein glycation and those which can lower postprandial blood glucose elevation are of utmost importance in minimising the damage caused by diabetes. One objective of this study was to assess the in vitro inhibitory effects of Syzygium cumini (SC) leaf extracts on protein glycation and α-glucosidase activity. The other objective was to identify the type of inhibition on α-amylase activity. SC leaf powder was sequentially extracted with hexane (H), ethyl acetate (E), methanol (M) and water (W). In vitro inhibitory effects of extracts on protein glycation, α-amylase and α-glucosidase enzymes were measured. M and W were the major fractions recovered [50.74 and 27.94 % (w/w), respectively] while H was the smallest fraction [7.35 % (w/w)] out of total yield. All extracts inhibited fructosamine formation, protein glycation and protein crosslinking at 2 mgmL -1 . At 0.05 mgmL -1 , fructosamine formation was inhibited in the presence of E, M and W while there was no significant inhibition with H. At 0.1 mgmL -1 , antiglycation effect of the H extract was negligible while other extracts retained their effects. IC 50 values of H, E, M and W extracts against α-glucosidase were 7.89, 3.11, 0.86 and 0.69 µgmL -1 , respectively. A mixed type inhibitory effect was observed on α-amylase with E, M and W extracts. H extract did not inhibit α-amylase. In conclusion, the results provide evidence for antiglycation and hypoglycaemic effects of SC leaf extracts demonstrating better activities in E, M and W extracts.
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